Passage Summary: The government asked kids to promise not to drink, and since the kids who don't drink are the ones who signed the promise, the government thinks the plan is working great.

Conclusion: The Department of Health's pledge program is effectively reducing underage drinking.

Reasoning: A survey shows a strong correlation between having taken the pledge and not drinking, while those who drink generally haven't taken the pledge.

Analysis: This argument falls into the trap of 'self-selection bias,' assuming the pledge *caused* the behavior when it's more likely the behavior determined who took the pledge. It's like concluding that 'No Smoking' signs in a library are the reason people aren't smoking there, ignoring the fact that people who want to smoke simply don't go to the library. The survey only shows that non-drinkers are willing to sign a piece of paper saying they won't drink. Look for an answer that points out the failure to consider that the pledge-takers were already predisposed to avoid alcohol.